Monocyte-derived macrophages support alveolar regeneration via oncostatin M post-H1N1 infection during the recovery phase

Severe influenza virus infection often triggers acute lung injury, and the efficacy of respiratory functional recovery critically depends on timely alveolar regeneration. However, the cellular dynamics and regulatory mechanisms underlying post-infectious alveolar repair remain incompletely understood. Utilizing Sftpc-CreER; Rosa26-mTmG lineage-tracing model, we determine the main stem cell population responsible for alveolar regeneration following influenza-induced injury. Through integrated single-cell RNA sequencing (scRNA-seq), immunofluorescence, and electron microscopy approaches, we mapped cellular transcriptional landscapes and spatial interactions. Key macrophage-epithelial crosstalk was further investigated via in vitro co-culture systems and in vivo conditional depletion models using diphtheria toxin receptor-transgenic mice. Putative regulatory factors were predicted through ligand-receptor interaction analysis and functionally validated in ex vivo organoid models. In this study, we revealed that the severely damaged alveolar barrier after influenza virus infection was rebuilt by the proliferation and differentiation of residual type II alveolar epithelial (AT2) cells in an inflammatory niche. In particular, monocyte-derived macrophage (Mo-Macs) expand, displaying intimate spatial proximity with AT2 cells. In addition, the cellular transcriptional status determined by scRNA-seq revealed that Mo-Macs regulate epithelial cell proliferation. Mo-Macs promoted the formation of AT2 spheres in vitro. Moreover, Mo-Mac depletion resulted in delayed repair of the alveolar epithelial structure in vivo. In addition, the mechanism by which Mo-Macs regulate alveolar epithelial repair involves the secretion of oncostatin M (OSM), which stimulates p-STAT3 activation and promotes AT2 cell proliferation. Our findings revealed that residual AT2 cells act as stem cells in the alveolus and are regulated by Mo-Macs through OSM secretion. These findings increase our understanding of the role of inflammatory signals in regulating tissue repair after severe injury, which may provide a potential avenue for therapeutic intervention in recovered patients.